If you run a 20 MHz Z80 against a 20 MHz 6502, you'll find the 6502 performs WAY
(3x-5x) faster than the Z80. It's difficult to base a comparison on clock rate
alone. All 6502 memory cycles take 1 clock tick. Z80 memory cycles, aside from
M1, take 3 clock ticks, with no wait states in use. If you run the 6502 at a
rate that fully utilizes the memory bandwidth at a rate such that the Z80 can
perform an M1 in the same amount of time, without wait states, the 6502 will
always be faster, because it's running faster. The Z80 uses 1-1/2 clock ticks
to execute its instruction fetch. If that's to be memory access window for each
processor, and you run them both from static memory, and you allow minimal
recovery time, e.g. use 10-15 ns memory, (just for the comparison) then you can
use a 20 MHz Z80 and a 20 (actually 14) MHz 6502, and clock the 6502 with a 25ns
low, 75ns high clock, and drive the Z80 with a square 20 MHz. That will be a 10
MHz clock for the 6502 and a 20 MHz clock for the Z80. I'd submit that the 6502
will still run rings around the Z80, since it is still going to be cycling
memory at an average of 200 ns per cycle, while the 6502 does it a 100 ns rate.
Surely a better comparison can be arranged.
Dick
----- Original Message -----
From: "ajp166" <ajp166_at_bellatlantic.net>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, December 19, 2001 4:46 PM
Subject: Re: MITS 2SIO serial chip?
> >Ben Franchuk <bfranchuk_at_jetnet.ab.ca>:
> >
> >> what is the faster CPU -- A 6502 or Z80 style processor like
> >> the rabbit.
>
>
> Depends...
>
> For the same instruction execution rate (ignores clocks and cycles)
> the z80 is likely faster. However... if you have a 20mhz 6502 and
> a 10mhz z80 it gets muddier with the 6502 being the faster. And
> if you know one better than the other you can certainly exploit it
> all the more. In the end it's not which one does a task faster, it's
> what one you can code the task for faster.
>
> Sorta like asking apples or oranges.
>
> Allison
>
>
>
Received on Thu Dec 20 2001 - 02:57:57 GMT